1. Field of the Invention
The invention generally relates to a projection apparatus and a projection lens.
2. Description of Related Art
With the development of technique, various kinds display apparatus different from the conventional cathode ray tube (CRT) display apparatus has been researched and promoted. The display apparatus includes a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting diode (OLED) display, and other panel display. In addition, the researched promoted display also includes a projector, a rear projection display, and other projection apparatus.
Although the LCD and the PDP are the main displays in the daily life now, the projection apparatus may provide a large size image (for example more than 52 inches) with lower cost, so the projection apparatus may not be replaced in large size image display. In addition, with the development of manufacture technique, the manufacture of the projector develops with lower cost and price. The present projector is used in the office, education place and research department. Meanwhile, it is a popular trend that a family has a home theatre with a projector.
With respect to the projection apparatus, an illumination system is used to form an illumination beam illuminating on a light valve, and the light valve converts the illumination beam into an image beam. A projection lens is disposed in the transmission path of the image beam to project the image beam to form an image on the screen.
With respect to the projection apparatus, an anamorphic lens is used to achieve some specific optical effect, or improve the optical quality. For example, a wedge prism disposes between a light combining prism and the projection lens to correct the colour difference and aberration generated by the prism in U.S. Pat. No. 6,299,312. In the other sides, a wedge prism in the projection system disposes before the display to deflect the direction of the light beam in U.S. Pat. No. 6,688,748. The display tilts an angle to correct the distortion, and the centre position of the display deviates from the optical axis to perform the optimization of the projection image.
An image distortion correction prism disposed between a dichroic cross prism and the projection lens to correct aberration in U.S. Pat. No. 6,478,429. In addition, two cylindrical lenses in the projection lens to improve the length-width ratio of the projection image in U.S. Pat. No. 6,512,636.
Although the disposition of the above-mentioned anamorphic lens solves some problem of the projection apparatus and improves the optical quality, the following problems still have not been solved.
Due to the projection apparatus is usually disposed on the desk or ceiling mounts and projects the image beam to form the image on the screen, the image beam may deviate from the optical axis of the projection lens so as to the image deviates from the optical axis for avoiding the image beam projecting on the desk or ceiling. In conventional method, the light valve deviates from the optical axis, so as to the image beam emits atilt from the optical axis of the projection lens and the image also deviates from the optical.
In addition, adopting the mentioned technique, the deviation of the light valve is similar to the deviation of the image. For example, if we want to the image deviate an offset of Z % from the optical axis, the light valve may deviate an offset of Z % from the optical axis.
However, excess offset of the light valve may result in excess maximum field of the projection lens to cause the outside diameter of the lens in the projection lens hard to reduce and then forms too large volume of the projection lens and the volume of the projection apparatus.